1. Field of the Invention
The invention relates to vehicle headliners. In one of its aspects, the invention relates to a vehicle headliner. In another of its aspects, the invention relates to a laminate construction for a vehicle headliner that optimizes formability, sound absorbing properties and structural integrity of the vehicle headliner.
2. Description of the Related Art
Vehicle headliners on the interior of an automobile are a decorative panel which separates the passenger compartment from the sheet metal forming the roof of the vehicle. The vehicle headliners absorb sounds from within the passenger compartment as well as sounds originating outside the passenger compartment. Soft fibrous materials are typically used for this function, but must be stiffened to give the headliners sufficient structural rigidity to avoid sag in service under all types of service conditions. It is further important that the overall thickness of the headliner be relatively small to maximize headroom within the vehicle compartment. In many applications, it is expected that the headliner will be sufficiently strong to support its own weight.
Previous commercial headliners have been made with fiberglass batting which is impregnated with a thermosetting resin for rigidity. Some of these panels have been relatively brittle and have failed when installed into vehicles. Further, glass fibers can cause handling problems. These headliners are typically not recyclable.
The required headliner properties of sound absorption, rigidity, and minimum thickness often conflict with each other and compromises must be made to reach optimum properties. Sound absorption is most easily obtained by making the headliner from a low density material that absorbs the sound waves as they enter the headliner and minimizes reflection of the sound waves as would more dense materials. In general, the greater the thickness of the low-density material, the greater the sound absorption but, thicker materials have a greater tendency to sag and adversely affect headroom. Generally, dense materials are used to provide the headliner with the necessary structural strength and rigidity for supporting its own weight and possibly mounting components to the headliner. More dense materials, in general, tend to reflect sound and thus, negatively impact sound absorption.
Some prior headliners have attempted to resolve the conflict between the sound absorbing and structural rigidity requirements for the headliner by making the headliner from a laminate of various materials, wherein some of the materials provide the structural rigidity and other of the materials provide the sound absorbing properties. One approach is to use a relatively low-density sound absorbing material sandwiched between two layers of reinforcing material. One of the reinforcing material layers has mounted thereto a decorative cover that forms the ceiling of the passenger compartment of the vehicle. An example of this structure, which is known as an I-beam construction, is disclosed in U.S. Pat. No. 4,828,910 to Haussling, issued May 9, 1989.
Most prior I-beam constructions use a thermosetting resin to bind together the various layers of the laminate. The resin is normally sprayed in liquid form on at least one of the abutting surfaces of the various layers. In general, the thermosetting resin negatively impacts the sound absorbing characteristics of the laminate because the resin can fill the interstitial spaces between the fibers in the laminate and thereby increase the reflectance of the sound waves instead of absorbing the sound waves. Thermosetting resins also make it more difficult if not impossible to recycle the laminate, which is an important characteristic and often a requirement of most components used in contemporary vehicle construction.
The U.S. patent to Weinle, U.S. Pat. No. 4,840,832, issued Jun. 20, 1989, discloses a headliner construction of a bicomponent fiber wherein the fibers are bonded together at their crossing points. The headliner is said to be so highly deformable and resilient that it can be bent or flexed nearly double to facilitate installation in an automobile side window and subsequently will resiliently recover to its original molded shape. Actual embodiments of these headliners have not had sufficient rigidity to avoid sag when subjected to elevated temperatures normally experienced in vehicles except when the mass and density of the headliners is very high, thereby negatively impacting vehicle fuel efficiency.
U.S. Pat. No. 6,066,388 to Van Kerrebrouck discloses a non-woven laminate comprising two outer fiber layers and at least one inner fiber layer having a different composition from that of the outer layers. The inner layer contains constructive fibers having a thickness of 3-100 dtex in combination with 20-100% binding fibers. The outer layers comprise constructive fibers having a thickness of 0.5-28 dtex in combination with 40-100% binding fibers. The thickness of the constructive fibers of the outer layers are thinner than the constructive fibers of the inner layer.
According to the invention, a laminate for use in making a thermoformed article comprises first and second strengthening outer layers and a core layer between the strengthening layers. The core layer comprises a bait of nonwoven thermoplastic fibers having 20-50% fine fibers by weight with a denier in the range of 0.8-3.0, 10-50% binder fibers by weight, and other fibers with a denier in the range of 4.0-15.0. Each of the strengthening layers comprises a bait of nonwoven polymeric fibers having more by weight coarser fibers than in the core layer. The strengthening layers provide the predominant flexural rigidity for the laminate and the core layer provides the predominant sound absorption for the laminate. The thermoplastic fibers can include polyester, polyolefin, and nylon. The polyester fibers preferably include bicomponent fibers, such as a PET sheath-core bicomponent fiber.
The binder fibers preferably have a denier in the range of 0.8-200, with a preferred range of 3-25 denier. The core layer batt has a basis weight in the range of 6-24 ounces/yd2, with a preferred range of 6-12 ounces/yd2. The core layer batt has a thickness of 0.5-2.0 inches, with a preferred thickness of 0.5-1.0 inches.
The laminate can further include first and second web adhesive layers that are positioned between each of the outer layers and the core layer. The web adhesive layers enhance the bonding between the outer layers and the core layer. Preferably, the web adhesive layer is a sheet of nonwoven polyester fibers.
The outer layers preferably comprise 50-100% by weight of thermoplastic fibers with a denier of 0.8-200 and 0-50% by weight of binder materials. The binder materials can include binder fibers. Additionally, the binder materials can include a thermosetting resin, which is preferably a thermosetting powder that is present in an amount up to 20% by weight of the outer layers.
The strengthening layers are preferably thinner than the core layer. The core layer has a greater resistivity than the strengthening layers. Preferably, each strengthening layer comprises less than 20% fine fibers and the core layer comprises at least 25% fine fibers. The percentage of fine fibers in each of the strengthening layers is preferably not greater than half the percentage of fine fibers in the core layer and the fine fibers of each strengthening layer not exceeding 20%.
Headliners made according to the invention have better sound absorbing properties and yet maintain the required structural rigidity properties, while minimizing thickness and density to maximize vehicle headroom and fuel efficiency, and are recyclable. Further, the headliners according to the invention are free of fiberglass and are flexible enough to avoid failure during installation and are less irritable to workers during handling, while satisfying requirements for low density and dimensional stability.
In yet another embodiment, the invention relates to a laminate comprising first and second strengthening layers and an intermediate core layer. Each of the strengthening layers comprises a batt of nonwoven polymeric fibers. The strengthening layers provide flexural rigidity for the laminate. The core layer provides sound absorption for the laminate and includes a batt of nonwoven thermoplastic fibers. The core layer batt preferably comprises 20-50% fine fibers with a denier in the range of 0.8-3.0, 10-50% binder fibers and the balance regular fibers with a denier in the range of 4.0-15.0, and. The first and second strengthening layers each comprise a batt of nonwoven polymeric fibers and have a density greater than the core layer.
The strengthening layers are preferably thinner than the core layer. The core layer has a greater resistivity than the strengthening layers. Preferably, each strengthening layer comprises less than 20% fine fibers and the core layer comprises at least 25% fine fibers. The percentage of fine fibers in each of the strengthening layers is preferably not greater than half the percentage of fine fibers in the core layer and the fine fibers of each strengthening layer not exceeding 20%.
In another embodiment, the invention relates to a laminate comprising first and second strengthening layers and a core layer disposed between the strengthening layers. The strengthening layers provide the predominate flexural rigidity for the laminate. The core layer provides the predominant sound absorption for the laminate. The core layer includes a batt of nonwoven thermoplastic fibers. The core layer batt comprises 20-50% fine fibers with a denier in the range of 0.8-3.0, and 10-50% binder fibers. The first and second strengthening layers each comprise a batt of nonwoven polymeric fibers and the core layer has a resistivity greater than at least one of the first and second strengthening layers.